Fine patterns are generally formed in the manufacturing process of semiconductor devices using photolithography. Normally multiple layers of substrates referred to as transfer masks are used to form these fine patterns. These transfer masks generally have a fine, thin film pattern composed of a metal thin film and the like provided on a transparent glass substrate. Photolithography is used to fabricate these transfer masks.
Accompanying remarkable improvements in the degree of integration of semiconductor devices in recent years, there is a growing demand for transfer masks that have increasingly fine patterns. Known examples of transfer masks include binary masks and phase shift masks. Binary masks are masks having a light shielding film pattern composed of, for example, a chromium-based material on a transparent substrate. Phase shift masks are masks in which a phase shifter portion is formed that generates a prescribed phase difference on a transparent substrate relative to exposure light. Phase shift masks are able to improve contrast at the interface between the phase shifter portion and light-transmitting portion, namely are able to improve resolution. A known example of this phase shift mask is a half-tone type of phase shift mask having a light semi-transmitting film pattern composed of, for example, a MoSi-based material on a transparent substrate. The light semi-transmitting film pattern allows transmission of light of an intensity that does not substantially contribute to exposure (for example, intensity of 1% to 30% relative to the exposure wavelength) and is also able to generate a prescribed phase difference (for example, 180 degrees) relative to the exposure light. In addition, another example of a phase shift mask is a Levenson-type phase shift mask as disclosed in Patent Literature 1. A Levenson-type phase shift mask is a substrate-engraved type of mask that can be provided with a phase shifter portion by engraving a transparent substrate by etching using a fluorine-based gas.
On the other hand, there is also a mask blank as disclosed in Patent Literature 2. The semi-transparent laminated film of this mask blank is obtained by laminating a phase-advancing film and a phase-retarding film. The phase-advancing film has the property of causing the phase of exposure light that has passed through the film to be advanced more than the phase of exposure light that passes through air by the same distance. Conversely, the phase-retarding film has the property of retarding the phase of exposure light that passes through the film. According to this type of configuration, exposure light that passes through the semi-transparent laminated film can be prevented from generating a phase difference with respect to exposure light that passes through air by the same distance. In the case of a phase shift mask fabricated using this type of mask blank as well, it is necessary to provide grooves engraved to a prescribed depth in the substrate surface. Dry etching using a fluorine-based gas is used to form these grooves.